Phosgene (also known as carbonyl chloride or carbonyl dichloride) finds use in the preparation of organic compounds, monomers, and polymers, such as carbonates, isocyanates, ureas, chloroformates, carbamates, polyurethanes, and polycarbonates. In one method for producing phosgene, carbon monoxide is reacted with chlorine in the presence of a carbon-comprising catalyst such as activated carbon or silicon carbide. The reaction is strongly exothermic and is usually performed in a reactor such as a multi-tubular reactor that has been designed similarly to conventional shell and tube heat exchangers.
A carbon tetrachloride by-product can result from the phosgene reaction and can be present in an amount of 50 to 300 parts per million (ppm) by volume or higher. The presence of carbon tetrachloride in the reactor can disadvantageously result in depletion of the catalyst. Furthermore, the presence of such high levels of carbon tetrachloride is disadvantageous in several applications where the level of carbon tetrachloride in phosgene needs to be less than or equal to 10 ppm by volume before use of the phosgene.
Phosgene purification to remove carbon tetrachloride can be difficult and is a significant part of capital investment and operating costs of any phosgene plant due to the costly material of construction of the purification equipment, the need for large enclosures to house said equipment, and further because the process is very energy intensive. On a global basis, the amount of byproduct carbon tetrachloride produced in commercial phosgene manufacture annually can be as much as 2 million kilograms based on phosgene production of about 4 billion kilograms.
A method to produce purified phosgene without the need for a separate purification process is therefore desirable.